Process for the preparation of 1-benzyl-5, 6, 7, 8-tetrahydroisoquinoline



Patented Sept. 8, 1953 UNITED STATES PATENT OFFICE PROCESS FOR THE'PREPARATION OF l-BEN- ZYL-J5,6,7,8-TETRAHYDROISOQUINOLINE Hans Henecka, Wuppertal-Elberteld, Germany,

assignor, by mesne assignments, to Farbenfabriken Bayer A'ktiengesellschaft, Lcverkusen- Bayerwerk, Germany No Drawing. Application December 9, 1950,, Se rial No. 200,121. .In Switzerland December 12,

1 11 Claims. (Cl. 260283) This invention relates generally totherapeutic It is also an object of this invention to pro; a ents useful as anal si to h r wi h procvide a method for synthesis of compounds of esses for making such agents. More particularth type ti ed hich will readily ermit 5 th nvention relat s to analgesic agents preparation of closely related alkoxy, especially which are closely related, both in chemical conmethoxy, substituted compounds by the mere stitution and therapeutic activity, to the opium selection of a suitably substituted initial reactalkaloid, morphine. ant.

It has been found that a chemical compound Regarded in certain of its-broader aspects, the designated y rph a e by Greweet al., novel process of this invention may be repre- Ber. 81, 279-86 (1948) and closely related tomorsented as follows: phine in chemical structure, produces analgesic effects and has other therapeutically useful properties almost as powerful as morphine itself- -o1n H Various procedures for the synthesis of this 7R l 11 compound have been proposed, as outlined in the 15 report of the investigations by Grewe et 21., con; H above cited, and in further reports by the same workers, but, in general these methods have had the common disadvantage of requiring organometallic compounds as intermediates that could H/\ 6 2* 5 a. H n

cated routes of organic synthesis, thus precluding use of these methods in commercial or large scale operations.

For example, it has been suggested to react benzyl magnesium chloride with N-methyl-5, l6, 7,8-tetrahydroisoquinolinium iodide, which may be prepared by treating .5,6,7 ,8-tetrahydroisoquinoline with methyl iodide, to produce .2- methyl 1 benzy-l 1,2,5,,6,'7,8 ,hexahyd-roisoquinoline, which may be converted to ;2-me.th y1- 1 'benzyl 1,2,3.,.4,5,,6,7,8 .octahydroisoquinoline by catalytic hydrogenation, then causing this compound to undergo intramolecular rearrangement and cyclization by heating it with about ten times its weight .of syrupy orthophosphoric acid at 150 .C. fora period of three days, to yield the desired N-methyl-morphinane. Another suggested process involves reaction of ,henzaldehyde with l-lithium-5,6,7,8-tetrahydroisoquinoline to produce the corresponding carbinol, reducing this .carbinol to 1-benzy-l-5,6, 7,8-tetrahydro-isoquinoline, treating it with be obtained only with difiiculty and by compli- H/ H methyl iodide .to form the corresponding quawherein Risatleast-one substituent of the-g oup ternary salt and thereafter reducing this salt (insisting-Of hy d y.

and then, by the intramolecular rearrangement d- 1m ore specific terms, but with refand cyclization above mentioned, obtaining the creme t0 foregoing yp thermadesired N-methyl-morphi-nane. ess of this invention comprises the condensation One of the chief objects of the present invenf a -t uv y h a yp -f u a tion is to provide a process for the synthesis of .60 MD, Which-may a n d by ester condensacompounds that may be utilized as intermediates @101! Of a p y ester ypein making N-methyl-morphinane and ,kindred with c'yfilohexa'none (WE u a I with substances, having the advantage over previouscyanacetamide ;to y d 1-b 'y y B, ly known methods of not requiring expensive .or 5,6;73hexailydrfi-isoq11in010nee3 (typ -f mu a diflicultly prepared raw materials or other inter- 5 IV), removing t nitrile su ituent 0f -this commed-iat pound by mild acid hydrolysis, for example by boiling with aqueous hydrobromic acid, treating this product (type-formula V) with a halogenating agent, for example with a phosphorus oxyhalide, to replace the 3-keto group with a halogen atom (type-formula VI), then reducing this halogen compound to obtain the desired l-benzyl-5,6,7,8-tetrahydroisoquinoline (type-formula VII). 3,5,6,7,8 hexahydro-isoquinolone 3 (type-formula V above) may also be prepared by condensing 11 cyclohexenyl-acetonitrile with phenacetyl chloride in the presence of an aluminum chloride catalyst to obtain NF-Z-(d-toluyl) cyclohexenyl-acetonitrile, which may be cyclized by heating with syrupy ortho-phosphoric acid to yield the desired product, as described and claimed in this inventors concurrently filed copending application, Serial Number 200,122.

The final product obtained by the process of this invention is useful as an intermediate in the synthesis of N-methyl-morphinane, to which it may be converted by treatment with methyl iodide to form the quaternary salt, reduction of this salt by catalytic hydrogenation to produce 2 methyl 1 benzyl 1,2,3,4,5,6,7,8octahydroisoquinoline and treatment of this compound to cause intramolecular rearrangement into the desired final product.

To illustrate an application of the principles of this invention, a typical process will now be described as an example, with the understandmg that, by use of suitable alkoxy substituted initial reactants, compounds useful in the synthesis of methanol is evaporated in vacuo, the crystalline The intermediate compoundl-benzyl-Z,

alkoxy substituted N-methyl-morphinanes may be obtained.

Example 33.? grams of 2(a-toluy1)-cyclohexanone (boiling point: 145 C. at 0.9 mm. pressure; melting point of the copper salt: 1513-154 C.) which may be obtained by condensation of cyclohexanone with phenylacetic acid methyl ester using sodium methylate as condensing agent, is boiled with 14.2 grams of cyanacetamide, 400 cc. of acetone,

(d=1.49) for 15 hours, then the acid is evaporated in vacuo at 40-50 0., yielding a crystalline residue which, when treated with sodium acetate solution, yields 34.5 grams of 1-benzyl-2,3,5,6,'7,8- heXahydro-isoquino1one-3 and this product, after recrystallization from methanol or acetic acid of 50 per cent strength, is obtained as fine needles, melting at 245 C.

About 50 grams of this isoquinolone derivative are heated in a sealed tube for five hours at 155 C. with 250 cc. of phosphorus oxychloride and, after evaporating excess phosphorus oxychloride in vacuo at 60 C., a residue is obtained, from which 1-benzyl-5,6,7,8,-tetrahydro-3-chloro-isoquinoline precipitates when the residue is treated with ice water. The reaction product (boiling at 162 C. at 0.05 mm. pressure) is purified, either by distillation or by recrystallization from dilute methanol or a mixture consisting of ether and petroleum ether, to give bright crystals melting at 87-88 C.

Approximately 50 grams of this chloro-isoresidue is dissolved in weakly acidified Water and the base is precipitated from the clear solution by adding sodium hydroxide solution. The

product, 1-benzyl-5,6,'7,8-tetrahydroisoquinoline, is obtained as a somewhat viscous oil, boiling at 143 C. under 0.3 mm. pressure, which yields a picrate with the melting point 132 C. and an acid sulfate with the melting point 214 C. The yields amount to 36 grams.

Having thus described the subject matter of this invention, what it is desired to secure by Letters Patent is:

1. Process for the synthesis of intermediates for the manufacture of therapeutic agents that comprises condensing a phenylacetic ester with cyclohexanone to produce 2(a-to1uyl) -cyclohexanone, reacting this product with cyanacetamide to form 1-benzyl-2,3,5,6,7,S-hexahydro--cyanoisoquinolone-3, subjecting this product to hydrol ysis under mildly acidic conditions to effect removal of the substituent cyano group, reacting the product with a phosphorus oxyhalide to replace the substituent 3-keto group with a halogen substituent, reducing this halogen compound by catalytic hydrogenation and recovering l-benzyl- 5,6,'T,8-tetrahydroisoquinoline from the reaction mixture.

2. The process as defined in claim 1 wherein the phenylacetic ester is condensed with cyclohexanone in the presence of an alkali metal alcoholate.

3. The process as defined in claim 1 wherein the 2-(a.-toluyl) -cyclohexanone is reacted with cyanacetamide in the presence of an alkali carbonate.

4. The process as defined in claim 1 wherein the hydrolysis of the 1-benzyl-2,3,5,6,7,S-hexahydrol-cyano-isoquinolone-S is effected by heating with aqueous hydrobromic acid.

5. The process as defined in claim 1 wherein the phosphorus oxyhalide isphosphorus oxychloride.

6. The process as defined in claim 1 wherein the catalytic hydrogenation is efiected by direct action of hydrogen in the presence of an activated palladium on charcoal catalyst.

7. A process for the synthesis of intermediates for the manufacture of therapeutic agents, comprising a step that comprises condensing a phenylacetic ester with cyclohexanone in the presence of an alkali metal alcoholate to produce 2-(atoluyl) -cycloheXanone.

8. A process for the synthesis of intermediates for the manufacture of therapeutic agents, comprising a step that comprises reacting 2-(atoluyD-cyclohexanone with cyanacetamide in the presence of an alkali carbonate to form 1- benzyl-2,3,5,6,7,8-heXahydro-4 cyano isoquinclone-3.

9. A process for the synthesis of intermediates for the manufacture of therapeutic agents, comprising a step that comprises hydrolyzing l-ben- Y y 0- -cyano-isoquinolone-3 to produce 1-benzyl-2,3,5,6,7,8-hexahydro-isoquinolone-Ii.

10. A process for the synthesis of intermediates for the manufacture of therapeutic agents, comprising a step that comprises reacting l-benzylfor the manufacture of therapeutic agents, com- 5 prising a step that comprises catalytically hydrogenating 1-benzy1-3-ch1oro-5,6,7,8-tetrahydroisoquinoline and recovering 1-benzy1-5,6,'7,8- tetrahydro isoquinoline.

HANS HENECKA.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Schnider et a1. May 29, 1951 Number FOREIGN PATENTS Country Date Switzerland Dec. 1, 1948 OTHER REFERENCES Basu et a1: Annalen, vol. 516, pp. 243-248 (1935).

Grewe et a1.: Berichte, vol. 81, pp. 279-286 (1948).

Number 

1. PROCESS FOR THE SYNTHESIS OF INTERMEDIATES FOR THE MANUFACTURE OF THERAPEUTIC AGENTS THAT COMPRISES CONDENSING A PHENYLACETIC ESTER WITH CYCLOHEXANONE TO PRODUCE 2-(A-TOLUYL) -CYCLOHEXANONE, REACTING THIS PRODUCT WITH CYANACETAMIDE TO FORM 1-BENZYL-2,3,5,6,7,8-HEXAHYDRO-4-CYANOISOQUINOLONE-3, SUBJECTING THIS PRODUCT TO HYDROLYSIS UNDER MILDLY ACIDIC CONDITIONS TO EFFECT REMOVAL OF THE SUBSTITUENT CYANO GROUP, REACTING THE PRODUCT WITH A PHOSPHORUS OXYHALIDE TO REPLACE THE SUBSTITUENT 3-KETO GROUP WITH A HALOGEN SUBSTITUENT, REDUCING THIS HALOGEN COMPOUND BY CATALYTIC HYDROGENATION AND RECOVERING 1-BENZYL5,6,7,8-TETRAHYDROISOQUINOLINE FROM THE REACTION MIXTURE. 